Hansen et al., J. Chem. Soc., Perkin Trans I, (1992), pages 1807-1810 teach various 4,5-dimethyl-1,3-dithiolo-2-one (or thione) maleimides corresponding to the formula ##STR2## wherein R represents --H, substituted phenyl, benzyl, or a C.sub.1 -C.sub.2 or C.sub.6 alkyl radical and Z represents oxygen or sulfur. These compounds are taught as having "electron-acceptor" type behavior.